the key words to search for are "high mass" vs. "low mass". you'll get a ton of stuff, as it's apparently a long-raging debate.I've searched and searched here, with many hits on which bridge to get but no answers to the why. It's quite possible I've been looking in the wrong area, but I decided to just post the question and get the info.
i like low-mass done right, which to me means something like a vintage fender threaded rod bridge or the first generation american standard bridge; the multi-grooved saddles allowed for correct string spacing, the saddles themselves were real steel for clarity and sustain, and the design allowed for the outer strings to "squeeze" the saddles in towards the center, causing the 4 saddles to be held against each other by the string tension, eliminating drift and rattle.
later fender bridges (and current mexi bridges) with the single groove in the center of each saddle fail on all counts, as the saddles are not steel, they will not space the strings right for jazz bass pickups, and they do not touch each other, allowing them to slide around, rattle and sink

